function messageMove(obj,target){
    var Timer = null;
    obj.onmouseover = function(){
        clearInterval(Timer);
        Timer = setInterval(function(){
            var speed = (target-obj.offsetTop)/10;
            speed = speed>0?Math.ceil(speed):Math.floor(speed);
            if(obj.offsetTop==target){
                clearInterval(Timer);
            }else{
                obj.style.top = obj.offsetTop + speed +"px";
            }
        },30);
    }
}